20. ORGANIC GEOCHEMISTRY OF DSDP LEG 47A, SITE 397 EASTERN NORTH ATLANTIC: ORGANIC PETROGRAPHY AND EXTRACTABLE HYDROCARBONS

The quantity, type, and maturity of the organic matter were de-termined for 45 samples of continental rise sediments from the Neogene and Lower Cretaceous at DSDP Site 397, eastern North Atlantic. Kerogen concentrates were described by microscopy, and vitrinite reflectance values were determined (33 samples). The hy-drocarbons in lipid extracts were analyzed by gas-chromatography (GC) and combined gas chromatography-mass spectrometry (GC-MS) (12 samples). Allochthonous lower Miocene mudstones proved the most or-ganic rich: both «-alkane distributions and kerogen microscopy in-dicated a mixed aquatic and terrestrial organic content. A domi-nance of phytane over pristane suggests a reducing environment of accumulation. These allochthonous-reduced sediments, slumping from the shelf edge to the continental rise, provide evidence for a